CHROMATOGRAPHY

Forensic Science Project

Activity Objectives

During this activity you should be able to:

• Use visual examination to identify an authentic signature from forgeries
• Use chromatography to determine the colour composition of the ink in black felt pens
• Use chromatography to identify the black felt pen used to write a note found at a crime scene
• Use chromatography to identify the colours used in the coating of Smarties®

Procedure

Part 1 - Identification of the Authentic Signatures

Mr Davis had one incident where he violated lab procedures. The violation required Mrs. Essery to complete a laboratory violation citation which had to be submitted to Mr Stoddart, Science Department Head. However, Mr Stoddart received four citations and needs help determining which one is the authentic note. Your role in the investigation is to analyze the signatures on the citations received by Mr Stoddart to determine which note has the authentic signature. In your crime lab book justify which signature you feel was the authentic signature.

You may feel that the detection of a forgery by hand writing analysis is not really conclusive. You may need to prove a signature is a forgery by analyzing, through chromatography, the ink used to make the signature.

Part 2 - Paper Chromatography - Separating Black Ink
The following procedure shows you how to make a chromatogram

• Cut four strips of chromatography (filter) paper (approximately 17 cm long and 1.5 cm wide and the end to go in the water should be pointed) and place a black dot (about two cm up from the pointed end of the strip) from each of the four pens on each of the strips. Make sure you label each strip or chromatogram with a pencil so that you can tell each of them apart.
• Dip the end of the strip into a test tube of water making sure that the water level is below the dot. Do not let the dot go below the water level, or you will have to redo Part 2.
• Allow the water to soak up the strip and watch what happens to the ink. This may take 30 - 60 minutes. Take the strips out of the test tubes and let them dry. Once dry, relabel your strips and tape them into your forensic lab book. Your results will be used in Part 3.

Part 3 - The Mystery Note

• Cut out an individual letter from the mystery note provided and tape it to the filter paper with the ink facing the filter paper.
• Run the chromatography experiment and tape the chromatogram to your forensic lab book.
• Compare these results with the results in Part 2. Record which pen was used to write the note. What specific evidence enabled you to come to this conclusion.

Part 4 - What are the Colours in the Candy Coating?

• Make four chromatogram strips and collect four different coloured Smarties®. Record, in pencil, the colour of each on a chromatogram strip
• Wet the edge of the candy with a very small drop of water and rub its edge on a chromatography strip. Repeat this procedure rotating the candy to make a distinct dot on the chromatogram. The dot should be at approximately the same spot as the pen dot in Part 2.
• Repeat the last procedure with the other three candies on the other three chromatogram strips
• Run the chromatography experiment and observe the patterns produced on the strips.
• Attach the strips to your crime lab book. Below each strip identify the colours used to make the candy coating.

Reflections on the Activity

In your crime lab book, answer the following questions.

1. Explain how to construct a chromatogram
2. Explain why chromatography can be used to separate and identify different substances that appear to look the same.
3. Describe how chromatography could be used to solve a crime.
4. What are some possible sources of error in this lab?

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